1. Field of Invention
The present invention relates to a process using an inclined fluidized bed for performing mild coal gasification, and producing valuable products.
2. Background
Coal has served as a base material for the production of valuables products for many centuries. Dyes have been obtained from benzene, naphthalene, and anthracene; all common coal products. The pharmaceutical and pesticide industries have commonly employed coal tar components. Creosote from coal is a common wood preservative. Coal phenols have been employed as antiseptics. Coking has produced the by-products of ammonia and synthesis gases, while resins and early plastics came from coal oil.
In the early part of this century, processes for smoke abatement lead to the invention of coke and liquid products by low-temperature distillation. This work by Thomas Parker lead to the Coalite and Rexco Processes in England and the Disco Process in the United States.
Retort methods for coal gas production, such as the Parker, Phurnacite, and Krupp-Lurgi processes, appeared in the decades of 1920 and 1930. These were atmospheric pressure retorts heating coal indirectly through metal walls to temperatures about 650.degree. C. The beds were kept thin so as to heat uniformly and produce good-quality char for "smokeless fuel". These batch retorts were operated in large staggered blocks to produce a steady flow of char, tar and gas. The Coalite Chemical Products Works at Bolsover, England, processed over 300,000 tons of coal annually by using 448 retorts, and some of these retorts are still in use producing chemicals from coal tars. However, most batch systems were replaced by continuous ones after World War II.
Higher throughput resulted in the use of moving bed processes for low-temperature devolatilization from the 1930's on, but operating conditions were more critical and feed coal selection was important. Two common methods were to have vertical moving beds, or nearly horizonal rotary drums.
The Disco Process of Pittsburgh Consolidated Coal Company used such a horizonal rotary drum, indirectly heated, to produce balls of agglomerated coal which had been partially vaporized. However, precise control by carefully blending recycle char with coal feed and imposing temperature requirements was needed to keep excessive reactor wall caking from occurring. In 1949 such a plant was built that processes 1000 tons of coal daily.
In Germany and Japan the Lurgi-Spulgas process was used before and during World War II to make transportation fuel, feedstocks and chemicals. Here a downward flow of mildly caking coal at atmospheric pressure was directly heated by upward flowing flue gas to about 650.degree. C. Similar processes used the names Koppers Vertical Ovens, Mimura, Shimomura, Wanishi, and Knowles in Japan and Krupp-Lurgi, Geissen, Bursig-Geissen, and Rolle in Germany.
With the advent of an international distribution system for petroleum after World War II, low-temperature devolatilization of coal rapidly declined, and many such plants were shutdown. When the oil shortages of the 1970's appeared, increased interest in such processes reappeared, but now with the utilization of modern fluidized bed technology, which featured high sweep gas rates, small particle sizes and allowed rapid heating of high-volatile coals resulting in improved yields of coal tars. However, in Germany, Yugoslavia and England plants using the Lurgi-Ruhrgas processes were built from the late 1960's on. Here a screw-mixer is combined with a fluidized bed using recycle char mixed with the feed coal.
In the United States the development of synfuel processes occurred during the decade of the 1970's. The COED process used a series of fluidized beds to stepwise carbonize caking coals at higher and higher temperatures. The Clean Coke method utilized a fluidized bed devolatilizer, while an entrained bed reactor for flash devolatilization was employed by Occidental.
Currently the only known commercial low-temperature plants are in England, South Africa and India.
In the United States most recent development concentrated on high temperature, high pressure processes designed to produce maximum yields of liquid and gaseous products; however, economic concerns have not been favorable for commercial exploitation. Currently mild gasification plants are not competitive with petroleum in the United States, but England does have two operating facilities producing "smokeless fuel". Such processes produce char that is too weak and friable to support deep beds needed for blast furnaces; thus, using low-temperature char for coke production is not feasible. Yet, from an economic viewpoint, any char produced must be marketable.
By 1963 the Lurgi-Ruhrgas process had been modified to use lignite fines in Yugoslavia, and for producing char fines from high-volatile bituminous coal by briquetting in Germany in 1975 and England in 1977. However, coal tars from this process produced by flash devolatilization have been of poor quality consisting of heavy, highly aromatic components with high melting points. Further, the high dust content has been an additional problem.
Prior art United States patents covering the above mentioned concepts include:
______________________________________ U.S. Pat. No. Inventor Year ______________________________________ 2,639,263 Leffer 1953 2,773,018 Parry 1956 3,076,751 Minet 1963 3,394,463 Futer 1968 3,562,115 Dunlop 1971 3,574,065 Eddinger 1971 3,663,421 Parr 1972 3,951,856 Repik 1976 4,069,024 Fernandes 1978 4,326,857 Kato 1982 4,344,821 Angelo 1982 4,501,551 Riess 1985 4,512,777 Wild 1985 ______________________________________
Referring to the above list, Leffer discloses an early conventional fluidized bed to "distill" solid hydrocarbonaceous material. Parry discloses an externally heated conventional fluidized bed lignite system for its drying, preheating and devolatilization. Minet discloses a conventional fluidized bed system using steam and a temperature below 840.degree. F., or 449.degree. C., with recycle solids to avoid agglomeration. Futer discloses a nonfluidizing system of horizonal stair-step moving beds designed to effectively heat the material. Dunlop discloses a carbonization retort heated by a surrounding conventional fluidized bed. Eddinger discloses a series of increasing temperature conventional coal fluidized beds, using recycled gas and recycled char, obtaining a separation of liquid products that is recovered from each fluidizing stage. Parr discloses a series of concatenated slanting trays each holding fluidized particles to produce an upper retort section and a lower combustion section containing a plurality of sidestreams. Repik discloses a high oxygen content conventional coal fluidized bed to produce first non-agglomerative char, then activated carbon. Fernandes discloses a fixed high-sulfur coal bed to produce "clean" low-Btu gas using steam. Kato uses a simple inclined fluidized bed using hydrogen to react with coal under high pressure to produce high-Btu gas. Angelo discloses a rotating drum retort using steam to make activated carbon from coal. Riess discloses a conventional fluidized bed method of coal drying to obtain a better coal product. Wild discloses a method of treating synthesis gas under high pressure to separate aqueous and hydrocarbon streams.
The present invention, like many of the above, is designed to process coal. However, as will be shown subsequently, it uses inclined fluidized beds, not conventional fluidized ones at normal pressures, but recycled inert gases to produce selected products by proper use of selective temperature and heating rate controls.